Boron carbide ballistic armor modified with calcium boride,titanium and/or manganese

ABSTRACT

COMPOSITE CERAMIC ARMOR WITH IMPROVED BALLISTIC PROPERTIES. BASIC BORON CARBIDE ARMOR IS IMPROVED BY THE ADDITION TO THE BORON CARBIDE OF CERTAIN QUANTITIES OF CALCIUM BORIDE, TITANIUM AND/OR MANGANESE, OR A COMBINATION OF ONE OR MORE OF THESE WITH CHROMIUM OR BORON. IMPROVED BALLISTICS ALSO RESULT FROM A MULTILAYER CERAMIC FACEPLATE WHEREIN ONE OR MORE LAYERS OF THE ABOVE MODIFIED BORON CARBIDE IS COMBINED WITH A LAYER OF BORON CARBIDE TO FOR, AN INTEGRAL CERMAIC FACE PLATE.

United States Patent US. Cl. 161-193 9 Claims ABSTRACT OF THE DISCLOSUREComposite ceramic armor with improved ballistic properties. Basic boroncarbide armor is improved by the addition to the boron carbide ofcertain quantities of calcium boride, titanium and/or manganese, or acombination of one or more of these with chromium or boron. Improvedballistics also result from a multilayer ceramic face plate wherein oneor more layers of the above modified boron carbide is combined with alayer of boron carbide to form an integral ceramic face plate.

BACKGROUND OF THE INVENTION The invention relates to ceramic composites.More particularly the invention relates to ceramic composites suitableas armor plate for the protection of personnel and equipment fromballistic projectiles.

The utility of armor for the protection of personnel and equipment haslong been recognized and utilized. The most successful modern armor is acomposite structure consisting of a backing means or plate composed ofresinglass fabric laminate to which has been adhered a hard ceramic faceplate of e.g. boron carbide, silicon carbide, or aluminum oxide. Such acomposite armor is described in detail in United States Letters Patents#3,509,833 and #3,516,898. Hard ceramic faced composite armor is alsoknown which utilizes a metal backing in place of the aforementionedresin-glass cloth laminate backing, such as the metal backed ceramic ofUnited States Letters Patent #3,431,818 which includes such metals asaluminum, aluminum alloys, and titanium having hard ceramic face platesadhered thereto. The mechanism by which the aforementioned types ofarmor successfully defeat ballistic projectiles, such as armor piercingbullets, is explained in detail in the cited patents. In summaryhowever, it has been found that when a high velocity projectile such asa .50 caliber armor piercing bullet strikes the ceramic face plate ofsuch an armor composite, the oncoming projectile is shattered orblunted, frequently with an accompanying local shattering of the ceramicspreading outwardly from the point of impact. The residual energy of theshattered or blunted projectile and the energy imparted to the shatteredpieces of the creamic face is absorbed by the relatively resilient metalor glass-resin laminate backing The primary advantage to the ceramictype of armor resides in the fact that it has about a 4 to 1 weightadvantage over the prior art steel armor, i.e. a ceramic composite armorof a given weight per unit of protective area will have 4 times theresistance to penetration of high velocity projectiles as will a steelarmor plate of equal weight per unit of protective area, or in otherwords, ceramic armor provides a degree of protection equal to that ofsteel armor plate at about one-fourth of the weight of the latter.

Composite ceramic armor is amenable to being fabricated into manyprotective articles such as the personnel body armor of United StatesLetters Patent #3,559,2l0 and the protective aircraft seat of UnitedStates Letters 3,730,826 Patented May 1, 1973 ice Patent #3,581,620 aswell as protective structural components for ground vehicles andaircraft in the form of panels or the like to protect engines, fueltanks and other vital parts of the vehicle or aircraft.

SUMMARY OF THE INVENTION The ballistic property of hot-pressed boroncarbide armor can be substantially improved by addition to the boroncarbide molding powder of certain quantities of calcium boride,titanium, and/or manganese. Such improvements in ballistic propertiescan be realized by additions to the boron carbide powder of 10 to 45% byweight of one or more material selected from each of the followinggroups:

(a) calcium boride, titanium, and manganese; and (b) chromium, andboron.

The result is that for a given weight per unit of protective area, theso-called areal density usually expressed in pounds per square foot, thehot-pressed modified boron carbide ceramic plate of the presentinvention produces a composite armor with the backing that is up toabout 12% superior in its ballistic properties, i.e. it will resistpenetration of high velocity armor piercing projectiles travelling at avelocity approximately 12% greater than the velocity of projectileswhich the conventional boron carbide armor is capable of protectingagainst. The practical manifestation of the foregoing, and theimprovement over the prior art composite boron carbide armor, is that itprovides a composite armor system with about 12% more protectioncapability.

The ceramic face plate portion of the invention composite armor may bemade up entirely of hot-pressed boron carbide modified with calciumboride, titanium, or manganese or mixtures of titanium and manganese.

The ceramic face plate however, may be made up of only a layer of themodified boron carbide with the remainder of the thickness of theceramic plate being composed of conventional boron carbide. The modifiedboron carbide layer may be on the front or outer surface of" the ceramicplate, i.e. the surface which is impacted by the high velocityprojectile, or it may be on the back or back side i.e. the side which isadhered to the fiber glass or metal backing means or plate, or, themodified boron carbide portion may be sandwiched between two layers ofconventional boron carbide. Furthermore, the modified boron carbideportion of the ceramic face plate may be in more than one layer e.g. theface plate may be made up of two modified boron carbide layers betweenwhich is sandwiched a layer of conventional boron carbide. Whatevermight be the physical location of the modified boron carbide layer orlayers, it must be present in the ceramic face plate in the amount offrom about 20 to of the total weight of the ceramic face plate.

The hot-pressing process employed in the fabrication of the inventionceramic armor is conventional and well known as will be evident by thedetailed description of the hot-press process contained in the ensuingexamples. Similarly, the process used to form the multilayer ceramicplates, which preferably involves first cold-forming of each of thelayers followed by hot-pressing all of the layers together to form theintegral plate, is part of prior art. None of the processing involved isconsidered a part of the present invention.

The backing means or plate may be any of the known materials suitablefor the purpose. Such materials include multiple ply resin-glass fabriclaminate, metals such as aluminum, aluminum alloys, titanium and thelike, or even sheet steel, although the latter is obviously undesirablebecause of its weight. So too, the method of unitizing the backing meansand the ceramic face plate may be accomplished by any of the knowntechniques such as adhering the two with a polysulfide or epoxy adhesivewhich may or may not include a resilient energy absorbing interlayerbetween the backing means and the invention ceramic face plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the preferred mode ofpracticing the present invention, commercial grade boron carbide isemployed which is the same type of material used to fabricate the priorart boron carbide composite armor. A typical analysis of commercialgrade boron carbide is as follows:

Constituents: Weight percent Boron 76 Carbon 21 Boron oxide 1 Iron oxide0.5 Aluminum oxide 0.25 Copper oxide 0.1 Cobalt oxide 0.1 Calcium oxide0.2 Manganese oxide 0.1 Trace amounts of sodium, sulfur, silicon,titanium, chromium.

The foregoing does not preclude the use of either more deficient boronor boron rich types of boron carbide. Boron carbide with a molar ratioof 3.5 to 4.5 :1 would be operable. The particle size of the boroncarbide powder is not hypercritical but preferably ought to be in therange of 3 to 15 microns for the sake of attaining maximum densityduring the hot-pressing operation. The same is true of the particle sizeof the calcium bon'de'. titanium, and manganese modifiers. Theprocessing technology employed in the hot-pressing of the ceramic faceplates and that for the assembly of the face plate and the resin-fiberglass backing were the conventional ones and for the numerous examplesset forth below, were as follows:

Ceramic plate forming process A quantity of boron carbide powder orboron carbide powder blended with the desired weight percent of thecalcium boride, titanium, and/or manganese modifier is dampened with 28percent by weight of a 48 percent by weight aqueous emulsion of Amprol#24, an emulsifiable wax sold by Merck & Co. Inc. The dampened powder isthen dried at about 82 C. to remove the water.

A predetermined amount of this molding powder, that amount sufficient toresult in a hot-pressed plate approximately 6 x 6 x 0.3 inches, isplaced in a mold and pressed at approximately 1 ton per square inch atroom temperature resulting in a preform approximately 6 x 6 x 0.7inches. This preformed plate is then placed in a graphite mold assembly,and the assembly placed in an induction heated press where the contentsof the mold are subjected to a temperature of from 2000 to 2200 C. at apressure of approximately 1 ton per square inch, the entire hot-pressingcycle involving 1% to 2 /2 hours. The hot-pressing operation is carriedout preferably in the presence of a nonoxidizing atmosphere and evenmore preferably in an inert atmosphere such as argon. The hotpressedplate is then removed from the mold, flash and/or other imperfectionsare removed and the plate is assembled with the backing means or plate.

When the ceramic face plate is itself a composite, then the two or morelayers of the final plate are first coldformed in the following manner:Assuming that the ceramic plate is to be trilayered and is to weigh 900grams, then 300 grams of material A is placed in a mold, spread leveland then pressed at room temperature at about 1 ton per square inch; 300grams of material B is then spread level upon the previouslycold-pressed 300 g p he We layers are that co sed a before; finally, asecond 300 grams of material A is spread level upon the material Bsurface of the cold-pressed AB composite and this composite and thefinal layer is then cold-pressed as before. The multilayered coldpressedplate AB-A is then hot-pressed as described above.

Assembly of ceramic face plate and backing A standard 12 ply unsaturatedpolyester resin bonded fiber glass laminate of appropriate size, i.e. 6x 6 inches, is mildly sandblasted to provide an optimum surface foradhesion. The ceramic face plates and the backing pieces are warmed to arange of about 32 C. to 38 C. A thermosetting polysulfide adhesive isspread over the sandblasted surface of the backing with a serratedspreader. The ceramic face plate is then placed on the cement oradhesive coated surface and forced into the adhesive by pressing andmoving slightly by hand. Each composite is then clamped tightly in thecenter for 2 or 3 minutes to force out excess adhesive and air. Theexcess adhesive is removed and the composites, while still clamped, areheated at about 65 C. for 2 to 2 /2 hours in order to thermoset thepolysulfide adhesive. The resinfiber glass with ceramic face platecomposite is now a finished piece of ballistic armor.

Following the procedures outlined above, composite ceramic armor with 12ply fiber glass backing, was fabricated of various ceramic face platecompositions and having a variety of layer arrangements within the faceplates made of the various compositions described above. These weretested ballistically against standard boron carbide armor. The ballisticproperties of this type of armor are, amongst other things, highlydependent on the areal density (weight per unit area) of the compositeand the specific gravity of the materials making up the armor. Hereinthe same 12 ply backing was employed in all samples and the ceramic faceplate in all cases was about 0.3 inch thick. Thus the face platescomposed of calcium boride, titanium and manganese modified boroncarbide had a different specific gravity than the control composite madewith standard boron carbide. In the table to follow two columns ofrelative ballistic data appear. The relative ballistic data identifiedas Actual are based on the actual ballistic data measured, relative tothe reference standard boron carbide armor, ignoring the differences inareal density of the composite armor of the present invention ascompared to the reference standard boron carbide armor; the actual arealdensity is also shown beside the Actual relative ballistic results. Theballistic results of the invention composites corrected or adjusted toan areal density of 6.55 pounds per square foot, the areal density ofthe boron carbide reference standard, are shown in the column identifiedas Corrected. The Corrected ballistic data for the invention compositearmor thus shows the degree of superiority of said invention armor ascompared to the standard boron carbide armor for the same areal density.The superiority of the invention armor may be taken advantage of bydirect substitution of invention armor of the same areal density(weight) as the standard boron carbide armor for the latter thusproviding armor that will defeat ballistic projectiles travelling at agreater velocity than the standard boron carbide armor is capable ofstopping, or, substitute invention armor of a reduced areal density(weight) for the standard boron carbide armor thus reducing the weightof the armor employed while providing an equal degree of protection asis afforded by the heavier standard boron carbide armor.

In the following table of Examples, the data under Resistance toPenetration shows the capability of the invention ballistic armor toresist penetration by armor piercing projectiles in terms of percentrelated to the capability of standard prior art composite boron carbidearmor as unless otherwise indicated, the layers are each of equalweight, e.g. in a bilayer plate the weight of the B C layer is equal tothe weight of the modified layer.

6 3. The ballistic armor of claim 1 wherein said backing means is afiber glass-organic polymer laminate.

Layers in face plate Resistance to penetration 1 Cor- Actual, rectcd,Example Location Composition, wt. percent percent AD. percent ADJControl Single 100% B 6 100 6. 55 100 6. 55 1 do 23% CaBs 77% B40 102 6.34 107 6. 55 II do Mn B40 98 6. 29 107 6.65 ML. do 4% Ti 96% B40 1086.77 106 6. 55 ii t 8 7 B 927 B o ron a 0 4 Rear 7% 93% B40 112 6.76 1116.55

1 Percentages rounded 01f to the nearest whole percent. 2 AD. is arealdensity in pounds per square foot.

The preferred amounts of modifier for the boron car bide are 10 to 45%by weight of calcium boride, 2 to 10% by weight of titanium, and 2 to 7%by weight of manganese. Furthermore, although the foregoing descriptionof the preferred mode of practicing the present invention involves hotpressing of the ceramic preforms, cold-pressing to (form the preformsfollowed by sintering is also operable. The preference for hot-pressingarises from the capability of this method of consistently producingplates of maximum and uniform density.

While it is uncertain as to exactly what occurs between the boroncarbide and the additive or modifier during hot-pressing, it is clearthat the amount of calcium boride, titanium, and/or manganese addedinitially is substantially all present in the final product. Minoramounts of metallic titanium and manganese have been identified in thefinal product. Numerous hypothetical reactions between the calciumboride, titanium, and manganese additives and the constituents in thecommercial grade boron carbide may be written, however attempts toestablish the occurrence of these reactions have not been conclusive.Nevertheless, the addition of calcium boride, titanium, and/ ormanganese to boron carbide followed by the high temperature processingof these mixtures, results in ceramic plates with substantially improvedballistic properties as compared to the standard boron carbide compositearmor of the prior art.

What is claimed is:

1. A composite ballistic armor including a backing means and an integralpressed and sintered ceramic face plate, said face plate comprising 20to 100% by weight of one or more of a first type of layer, said firsttype of layer consisting essentially of a mixture of boron carbide and amaterial selected from the group consisting of calcium boride, titanium,manganese, and mixtures thereof, the remainder of said face plate beinga second type of layer consisting essentially of boron carbide.

2. The ballistic armor of claim 1 wherein said backing means is a metal.

4. The ballistic armor of claim 1 wherein said face plate consists ofone of said first type of layer and one of said second type of layer.

5. The ballistic armor of claim 1 wherein said face plate consists oftwo of said first type of layer separated by one of said second type oflayer.

6. The ballistic armor of claim 1 wherein said first type of layerconsists essentially a mixture of 10 to 43% by weight of calcium borideand 55 to boron carbide.

7. The ballistic armor of claim 1 wherein said first type of layerconsists essentially of a mixture of 2 to 10% by weight of titanium and90 to 98% by weight of boron carbide.

8. The ballistic armor of claim 1 wherein said first type of layerconsists essentially of a mixture of 2 to 7% by weight of manganese and93 to 98% by weight of boron carbide.

9. A composite ballistic armor including a backing means and an integralceramic face plate, said face plate comprising 20 to 100% by weight ofone or more of a first type of layer, said first type of layerconsisting essentially of a mixture of 10 to 45% by Weight of one ormore material selected from each of the groups:

(a) calcium boride, titanium, and manganese; and

(b) chromium, and boron; with 55 to 90% by Weight of boron carbide, theremainder of said face plate being a second type of layer consistingessentially of boron carbide.

References Cited UNITED STATES PATENTS 3,516,898 6/1970 Cook 161933,649,342 3/1972 Bartlett 161-404 X 3,671,374 6/1972 Kolarik l61404 XROBERT F. BURNETT, Primary Examiner M. F. MCCAMISH, Assistant ExaminerU.S. Cl. X.R. 75-204; 89-36; 10643; 161-43, 196, 225, 404

